Backscattering Spectroscopy: How it all began

 

Winfried Petry and Bernhard Frick asked me to say a few personal words before Andreas Magerl starts his talk about the history of backscattering spectroscopy.

 

 It is a great pleasure for me to be here with you in this workshop. I am very happy that my old friend and thesis companion Manfred Birr sits here in the first row and shares with us this event. 50 years ago in spring 1966 we both obtained our diploma degree in physics at the Technical University in Munich. After a 6 months long holiday period ( I went with 2 friends by car to Nepal, Manfred to Russia) Manfred and myself started our thesis together at the Institute of Maier-Leibnitz ( ML) at the FRM Reactor in Garching. We were called the ‘twins’ by the secretary of ML. Our task: development of a new kind of neutron spectrometer on the basis of backscattering: Das Rückstreu-Spektrometer. This was the common part of our thesis. Then each of us should use this new instrument to do new science.

 

Soon after we had started, ML became the Director of the ILL. So Berthold Alefeld, also a thesis student of ML, became our tutor.

The atmosphere at the institute of freedom was fantastic. We, three thesis students, were the’owners’ of the Mess-Haus, a wooden barrack. We had to give an oral progress report to ML from time to time, when he was in Garching on visit (Vorsingen).

 

The instrument was operational in 1968 and presented at the IAEA in 1968 in  Kopenhagen in a short paper (ABH).

 

 Science: Manfred choose QNS in plexi-glass (PMMA) and in liquid glycerol. He did not know at that time that his experiments opened a new field of research, namely the study of soft matter with neutron spectroscopy: Polymers, biophysics, chemistry, the glass transition etc. The results on glycerol were in striking disagreement with older neutron results by Larson et al. But both were correct. This shows that that a sentence attributed by T.Springer to Maier-Leibnitz is true: 

 

 The development of a new method, when ever its precision, sensitivity or resolution is much better than everything that existed in this field before, creates « new physics ».

 

I choose the study of hyperfine interactions by inelastic spin-flip scattering. The experiment on magnetic V2O3 was successful. The quadrupole experiment in As2O3 was negative and still is today! It is still my dream that someone will publish a positive result of this phenomenon! Bernard Frick tried 2 months ago to measure the quadrupole split neutron spectrum in solid Iodine on IN16B, again negative: he found that the spin dependent scattering cross section of Iodine is 1 to 2 orders of magnitude smaller than the literature value!

I have another dream which is the measurement of nuclear spin waves with INS. But not so many scientists are today interested in this field which still fascinates me. I am very happy that Bernard Frick , Tappan Chatterji and some others are doing experiments along these lines. Their discovery that Nd nuclei are very well suited for these studies is great. Recent experiments with the instrument Basis at the spallation source in Oakridge on Ho compounds is another breakthrough.

 

Before I stop to pass over to Andreas, a few words about people who were very important in the development of backscattering in its early stage:

Heinz Maier-Leibnitz, Tasso Springer and Berthold Alefeld.

ML was the first who had the idea, one among many others.

Tasso Springer was a believer in BS: It was him who sponsored the construction of IN10 from his Institute IFF in the KFA Jülich in 1973.

 

Berthold Alefeld.    

    I would like to dedicate this welcome to the late Berthold Alefeld. He was an outstanding experimentalist who produced an incredible number of new ideas in this field. One important example was his proposal of a phase space transformer PST. Berthold had what I call the scientific instinct. He felt physics. Berthold was also a very ambitious scientist.

He was keen to perform new experiments and he has done many together with his thesis students using the BS technique. Examples in condensed matter physics:

Tunnelling of CH3 groups in di-methyl-di-acethylene.

Self-diffusion in a sodium single crystal.

Reorientation of NH4 groups in molecular crystals.

Motions in plastic and liquid crystals

Hydrogen diffusion in metals.

Examples of fundamental physics experiments:

Neutrons in the gravitational field.

Longitudonal Stern-Gerlach effect.

Neutron magnetic resonance shift.

A perfect crystal storage device.

Examples in instrument development:

GaAs crystals as BS monochromators

Temperature gradient monochromators

PST as mentioned above.

Berthold  Alefeld thought that the author sequence on a paper is very important and he was embarrassed about his initial A because he was also a very modest man. He was a fighter and liked competition. He enjoyed playing tennis. I remember many years ago he told me that he had just finished writing a paper about the theory of the tennis game! He claimed that this paper was the best publication he had ever written!

I consider Berthold Alefeld as the father of backscattering spectroscopy.

 

Manfred and myself, we are just two of his scientific sons. Some grand sons are here today: I will mention only two of them:

Winfried Petry and Andreas Magerl who worked as post docs with me at the ILL. By the way I must say that very often I have been very lucky with my collaborators. Quite a number of then climbed high up the ‘leader of fame’. I should not forget my friend Dieter Richter who had an important impact on the development of BS. But Dieter as another believer in high resolution neutron spectroscopy became later also a very strong supporter of the Neutron Spin Echo technique.

 

 The competition between BS and NSE was certainly very positive for the development of both techniques.

 

 Using the backscattering technique for x-rays is another success story. Please have a look at the instrument of Francesco Sette at the ESRF in Grenoble.

 

 Let me finish by saying that I am looking forward with curiosity to listen to the presentations of scientific results and new developments in the field of neutron BS. 50 ago we certainly could not imagine what had happened since. Manfred and myself, we consider ourselves as lucky guys who participated in opening a new field.  This does not happen very frequently to thesis students.

 

 

Anton Heidemann, 2.September 2016